JP4074714B2 - Array type light modulation element and flat display driving method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an array type light modulation element that is manufactured by micromachining and changes the light transmittance by an electromechanical operation, and a method of driving a flat display using the array type light modulation element. The present invention relates to a technique for improving the response speed of an element and a flat display.
[0002]
[Prior art]
An electromechanical light modulation element that performs light modulation by mechanically operating a flexible thin film manufactured by micromachining by electrostatic force is known. As this light modulation element, for example, there is one in which a flexible thin film made of a transparent electrode and a diaphragm is installed on a fixed electrode on a light guide plate through a support portion.
In this light modulation element, by applying a predetermined voltage between both electrodes, an electrostatic force is generated between the electrodes, and the flexible thin film is bent toward the fixed electrode. Along with this, the optical characteristics of the element itself change, and light is transmitted to the light modulation element. On the other hand, by setting the applied voltage to zero, the flexible thin film is elastically restored, and the light modulation element blocks light. In this way, light modulation is performed.
[0003]
By the way, when the flexible thin film is deformed by an electrostatic force or elastically restored, the relationship between the applied voltage Vgs and the displacement of the flexible thin film exhibits a hysteresis characteristic. Accordingly, the relationship between the applied voltage Vgs and the light transmittance T also exhibits hysteresis characteristics as shown in FIG.
According to this hysteresis characteristic, when the light modulation element is in the OFF (light shielding) state, the OFF state is maintained when Vgs is equal to or lower than Vth (L), and the ON state is maintained when Vgs is equal to or higher than Vth (H). The light modulation element remains in the ON state when Vgs is equal to or higher than Vth (H), and is saturated to the OFF state when Vgs is equal to or lower than Vs (L). In addition, when the polarity of Vgs is negative, the characteristics are positive and symmetric with respect to the vertical axis.
[0004]
[Problems to be solved by the invention]
Based on the hysteresis characteristics, Vs (H) is applied as an applied voltage Vgs from an equilibrium state (OFF state) where no static stress is generated on the flexible thin film, and then Vgs is zeroed after the flexible thin film is sufficiently deformed. The response characteristics of the transmitted light are shown in FIG.
[0005]
According to FIG. 18, the rise time τr due to voltage application has a fast displacement response due to electrostatic force (attraction), and the optical response due to this is also fast. Furthermore, the response time can be shortened by increasing the applied voltage Vgs.
On the other hand, the fall time τf is an elastic recovery time determined by the material and shape of the flexible thin film, and is generally later than the rise time τr. Moreover, control by the applied voltage is naturally impossible.
[0006]
For this reason, when the light modulation element is driven in a two-dimensional matrix, the scanning time τ for writing the image signal to be input to the light modulation pixel is limited by the slower response time. In the above example, the scanning time τ is the falling time τf. As described above, when the scanning time is delayed, the number of rows of the matrix cannot be increased, and in the driving method for obtaining the gradation by time division, there is a problem that the number of gradations cannot be increased. Become.
[0007]
Furthermore, in the case of such a hysteresis characteristic, since the next operation is affected by the state of the flexible thin film before writing, in order to perform the writing operation with good reproducibility, reset before the writing operation. It is desirable that the operation, that is, the equilibrium state (OFF state) is once performed and then the writing operation is performed so as to obtain a desired transmittance. However, if the reset operation is simply performed before the writing operation, the scanning time per row is further increased, and this problem is promoted.
[0008]
Therefore, it is conceivable that high-speed response can be obtained by increasing the rigidity of the flexible portion of the light modulation element. However, the drive voltage increases because the drive voltage increases, thereby reducing the cost and size. It can be a hindrance.
[0009]
The present invention has been made in view of such a conventional problem, and even if the electromechanical light modulation element has a long response time that requires a long time to return, the loss due to the return time without degrading the image quality. It is an object of the present invention to provide an array type light modulation device and a method for driving a flat display capable of preventing the above problem and dramatically improving the substantial response time.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the method for driving an array light modulation element according to claim 1 comprises:
In an array type light modulation element in which electromechanical light modulation elements that perform light modulation by an elastic force displacement operation and an elastic return operation of the flexible part are arranged in a two-dimensional matrix, the light modulation The reset scan for performing the element return operation is performed simultaneously with the write scan for selecting the displacement operation or the state maintenance for the scan lines other than the scan line to be reset, and the write scan for each scan line is performed without interruption. It is characterized by being driven.
[0011]
In this array type light modulation element driving method, reset scanning of the light modulation element is driven simultaneously with the writing scanning period for the scanning lines other than the scanning line to be reset, so that the writing scanning of each scanning line has a long elastic recovery. Even a light modulation element that requires time can be performed without loss of time, and the response time of the array type light modulation element can be dramatically improved.
[0012]
The array type light modulation device driving method according to claim 2 is characterized in that the reset scanning time is set to an integral multiple of the writing scanning time.
[0013]
In this array-type light modulation device driving method, the reset scanning time is set to an integral multiple of the writing scanning time, so that the reset scanning time can be extended by a simple design change without impairing the design freedom. Even an element that requires a longer elastic recovery time can be driven without lowering the response speed.
[0014]
According to a third aspect of the present invention, there is provided the method for driving the light modulation element, wherein the reset scanning driving time is set to be equal to or longer than the elastic return time of the flexible portion.
[0015]
In this light modulation element driving method, the reset operation is the elastic return operation of the flexible portion of the light modulation element, and the reset drive time is set to be equal to or longer than the elastic return time of the flexible portion. Therefore, it is possible to achieve a driving method that ensures the elastic return without being in the middle of the elastic return. Further, by bringing the reset driving time closer to the elastic recovery time, the element writing operation can be performed immediately after resetting, and the element can be driven efficiently.
[0016]
According to a fourth aspect of the present invention, there is provided the method for driving the light modulation element, wherein the elastic return operation of the light modulation element is an operation of entering a light shielding state after the return.
[0017]
In this method of driving the light modulation element, the light is turned off after completion of the elastic return operation, which is the reset operation of the light modulation element. Therefore, when performing the reset operation, the light remains blocked when outputting “black” as an image. When “white” is output, the output decreases only during the reset period, but there is almost no problem. On the other hand, when the reset operation is in a light transmission state, when “black” is output as an image, light transmission occurs due to the reset operation, and the contrast is significantly reduced. Therefore, such a decrease in contrast can be prevented.
[0018]
According to a fifth aspect of the present invention, there is provided a flat panel display driving method comprising: the array type light modulation element; a flat light source disposed opposite to the array type light modulation element; and an array type light modulation element on the opposite side of the flat light source. A fluorescent material provided, and driving the array type light modulation element by the driving method according to any one of claims 1 to 4 to cause fluorescence by light emitted from the array type light modulation element. The body is displayed in a luminous manner.
[0019]
In this flat display driving method, a light source that has passed through an array type light modulation element using an electromechanical array type light modulation element that completes a reset operation before the element write operation to increase the response time. Since the phosphor is configured to emit and display light, the flat display can be driven at high speed.
[0020]
The flat display driving method according to claim 6 is characterized in that the flat light source is an ultraviolet light emission light source for exciting the phosphor.
[0021]
In this flat display driving method, the emitted ultraviolet light from the flat light source can be transmitted and shielded by the light modulation element, and the phosphor can be excited to emit light.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a configuration of a light modulation element according to the first embodiment of the present invention.
[0023]
As an operation principle of optically modulating the flexible thin film by electromechanical operation, a light guide diffusion action (hereinafter referred to as light guide diffusion) by separating or contacting the flexible thin film and the transparent signal electrode is used. be able to. In light guide diffusion, when the gap is formed as a light transmission resistance, when the gap is formed, the emitted light from the signal electrode is blocked or attenuated, while only when the flexible thin film is brought into contact with the signal electrode, Light emitted from the signal electrode is guided (mode coupled) to the flexible thin film, and the light is diffused in the flexible thin film, thereby controlling the intensity of light emitted from the flexible thin film (modulating light).
[0024]
As shown in FIG. 1, one electrode (signal electrode) 2 that is transparent to ultraviolet rays is formed on the light guide plate 1. For example, a metal oxide such as ITO with a high electron density, a very thin metal thin film (aluminum, etc.), a thin film in which metal fine particles are dispersed in a transparent insulator, or a highly doped wide hand gap semiconductor is suitable. is there.
[0025]
An insulating support portion 3 is formed on the electrode 2. For the support portion 3, for example, silicon oxide, silicon nitride, ceramic, resin, or the like can be used. A diaphragm 4 is formed on the upper end surface of the support portion 3. A gap (cavity) 5 is formed between the electrode 2 and the diaphragm 4. For the diaphragm 4, a semiconductor such as polysilicon, insulating silicon oxide, silicon nitride, ceramic, resin, or the like can be used. The refractive index of the diaphragm 4 is preferably equal to or higher than the refractive index of the light guide plate 1.
[0026]
On the diaphragm 4, a light diffusion layer 6, for example, an inorganic or organic transparent material with irregularities formed thereon, a microprism, a microlens, an inorganic or organic porous material, or a refractive index A material in which different fine particles are dispersed in a transparent substrate is formed.
[0027]
On the light diffusion layer 6, the other electrode (scanning electrode) 7 transparent to ultraviolet rays is formed. As an example, a material similar to that of the electrode 2 can be used. The diaphragm 4, the light diffusion layer 6, and the electrode 7 constitute a flexible thin film 8 as a flexible part.
[0028]
A gap 5 exists between the light guide plate 1 and the diaphragm 4, and the gap 5 is substantially determined by the height of the support portion 3. The height of the gap 5 is preferably about 0.1 μm to 10 μm, for example. The void 5 is usually formed by etching a sacrificial layer.
[0029]
In addition to the above-described configuration example, the diaphragm 4 and the light diffusion layer 6 may be formed of the same material. For example, the diffusion function can be provided by configuring the diaphragm 4 with a silicon nitride film and forming irregularities on the upper surface.
[0030]
Next, the operation principle of the light modulation element 10 configured as described above will be described.
When the voltage is OFF, the voltages of both electrodes 2 and 7 are zero, and there is a gap 5 (e.g., air) between the diaphragm 4 and the light guide plate 1,
When the refractive index of the light guide plate 1 is nw, the total reflection critical angle θc at the interface with air is
θc = sin ^-1 (Nw)
It becomes. Accordingly, when the incident angle θ to the interface is θ> θc, the ultraviolet rays proceed while being totally reflected in the light guide plate 1 as shown in FIG.
[0031]
When voltage is applied to both electrodes 2 and 7 when the voltage is ON, and the diaphragm 4 and the surface of the light guide plate 1 are brought into contact with each other or close to a sufficient distance, as shown in FIG. Then, the light is further diffused by the light diffusion layer 6 and emitted to the surface side.
[0032]
According to the light modulation element 10 according to this embodiment, light modulation can be performed by position control of the diaphragm 4 by voltage application.
An electrode 2 that is transparent to ultraviolet rays exists between the light guide plate 1 and the diaphragm 4. However, if the thickness of the normally used thin film is about 2000 A, the above-described operational problems may occur. Absent.
[0033]
In the present embodiment, as shown in FIG. 2, the light modulation elements 10 are arranged two-dimensionally in n rows and m columns. That is, the light modulation elements 10 are respectively arranged at the intersections Tr (1,1), Tr (1,2), Tr (2,1), Tr (2,2) of the matrix, and the array type light modulation element 50 is arranged. Configure.
Each light modulation element 10 corresponds to one pixel region. Here, the description will be made by paying attention to a matrix of two rows and two columns which is a part of the matrix.
The array type light modulation element 50 operates by simple matrix driving.
[0034]
The respective electrodes of the light modulation elements 10 arranged in the same row are connected in common as scanning electrodes. A potential Vg is applied to the scan electrode. In addition, the respective electrodes of the light modulation elements 10 arranged in the same row are connected in common to serve as signal electrodes. A potential Vb is applied to the signal electrode. Accordingly, the interelectrode voltage Vgs applied to each light modulation element 10 is (Vb−Vg).
[0035]
In order to drive the array light modulation element 50, the scan electrodes 7 are scanned in a row sequence in accordance with the scan signal, and a data signal corresponding to the scanned electrode 7 is applied to the signal electrode 2 in synchronization therewith.
[0036]
Here, three types of signals (voltages) including a reset signal, a selection signal, and a non-selection signal are applied to the scan electrode 7.
The reset signal turns off (light shielding) the light modulation elements 10 in that row regardless of the previous state of the light modulation elements 10. The voltage of the scanning electrode at this time is Vg (r).
[0037]
The selection signal is a signal for writing data in the row (signal for writing operation). Simultaneously with this signal, the state of the light modulation element 10 is determined to be ON (light transmission) or OFF (light shielding) in accordance with the voltage applied to the signal electrode. The voltage of the scanning electrode at this time is Vg (s).
[0038]
The non-selection signal is a signal when no selection is made. At this time, the state of the light modulation element 10 does not change regardless of the voltage of the signal electrode, and the previous state is maintained. The voltage of the scan electrode at this time is Vg (ns).
[0039]
On the other hand, the signal electrode 2 is supplied with two types of signals (voltages), ie, an ON signal and an OFF signal.
The ON signal turns on the light modulation element 10 (light transmission) with respect to the light modulation element 10 in the selected row. The voltage of the signal electrode 2 at this time is Vb (on).
[0040]
The OFF signal turns off the light modulation element 10 (light shielding) with respect to the light modulation elements 10 in the selected row. However, actually, since it is assumed that the light modulation element 10 is reset immediately before, when the state of the light modulation element 10 is turned off (light shielding), the previous state (OFF state) is maintained. It may be a signal to The voltage of the signal electrode 2 at this time is Vb (off).
[0041]
The interelectrode voltage Vgs of the light modulation element 10 is divided into the following six types of voltage by the combination of the above scan electrode voltage and signal electrode voltage. Further, specific conditions are given by the characteristics of the interelectrode voltage Vgs and the transmittance.
[0042]
Vgs (r-on) = Vb (on)-Vg (r) ≤ Vs (L)
Vgs (r-off) = Vb (off)-Vg (r) ≤ Vs (L)
Vgs (s-on) = Vb (on)-Vg (s) ≥ Vs (H)
Vgs (s-off) = Vb (off)-Vg (s) ≤ Vth (L)
Vgs (ns-on) = Vb (on)-Vg (ns) ≤ Vth (L)
Vgs (ns-off) = Vb (off) -Vg (ns) ≥ Vth (H)
[0043]
The above conditions are summarized as shown in FIG.
For example, when the scan electrode voltage Vg is reset Vg (r) and the signal electrode voltage Vb is ON, that is, Vb (on), the signal electrode voltage Vb having a value larger than Vs (H) (thick solid line 61 in the figure). From this, the scan electrode voltage Vg (bold solid line 63 in the figure) between Vs (H) and Vth (L) is subtracted, and the value (bold solid line 65 in the figure) becomes smaller than Vs (L).
That is,
Vgs (r-on) ≦ Vs (L)
It becomes. In the same manner, six types of voltages are determined.
[0044]
Next, a method of writing data in a matrix in which the light modulation elements 10 are two-dimensionally arranged using such a relationship between the interelectrode voltage Vgs and the transmittance will be described.
Data is written using the matrix of 2 rows and 2 columns shown in FIG. 2 as the matrix. The following ON / OFF data is written in each light modulation element 10 of the matrix.
Tr (1,1) → ON Tr (1,2) → OFF
Tr (2,1) → OFF Tr (2,2) → ON
[0045]
A voltage having a waveform as shown in FIG. 4 is applied to the matrix.
For example, the first line Vg (1)
t1: Reset voltage t2: Selection voltage
t3: non-selection voltage t4: non-selection voltage
Is applied.
In the first row Vb (1),
t1: don't care t2: ON voltage
t3: OFF voltage t4: don't care
Is applied.
As a result, desired data is written in each light modulation element 10 in a row sequential manner.
Then, after the reset scan of the light modulation element, the write scan for selecting the displacement operation or state maintenance of the element is performed, thereby preventing the state before the write scan from affecting the next operation due to the hysteresis characteristic of the element. Therefore, stable writing scanning can be performed. Also, due to the hysteresis characteristics of the element, the two-dimensional light modulation array having a simple matrix configuration is driven without contradiction, that is, the pixels on the non-selected scanning lines are reliably maintained in the ON / OFF state set during the writing scanning. It becomes possible to do.
[0046]
That is, for example, in the case of the matrix Tr (1,1) in the above-mentioned first row and first column,
Since Vgs: Vb (1) -Vg (1),
t1: Reset voltage (OFF) t2: ON
t3: state maintenance t4: state maintenance
It becomes.
[0047]
Accordingly, the ON state at t2 is maintained (memory), and as a result, the light modulation element 10 is in the “ON” state in the matrix Tr (1, 1). Similarly, the other matrix Tr (1, 2) is in the “OFF” state, Tr (2, 1) is in the “OFF” state, and Tr (2, 2) is in the “ON” state.
[0048]
With the above operation, the application state of the scanning voltage to the light modulation element of each scanning line is as shown in the chart of FIG. In other words, a reset voltage and a selection voltage are sequentially applied to an arbitrary i-th scanning electrode, and in the i + 1-th scanning line, immediately after the selection voltage application period in the i-th scanning line ends, the selection voltage is immediately and without interruption. Is applied. In this case, the reset voltage application period of the (i + 1) th row overlaps with the selection voltage application period of the ith row. Similarly, the reset voltage application period is overlapped with the selection voltage application period of the previous row for the other scan lines.
[0049]
As described above, the light modulation element 10 of each scanning line performs a reset operation simultaneously with the selection period (writing period) of another row, thereby obtaining a stable writing operation without increasing the scanning time. Accordingly, it is possible to prevent the scanning time from being delayed due to the elastic characteristics of the flexible portion of the light modulation element and the application of the reset signal, and to increase the size and definition of the array type light modulation element while realizing reliable operation. Can do.
[0050]
Next, a second embodiment of the light modulation element driving method according to the present invention will be described. The present embodiment is a driving method in the case of using an optical modulation element in which the return time (fall time) τf is greatly delayed (τf >> τr). FIG. 6 shows the waveform of the voltage applied to each light modulation element. In the present embodiment, the reset voltage application period is set to three times that of the first embodiment. That is, in FIG. 6, the reset period t1 in the first row shown in FIG. 4 corresponds to t1 to t3 in FIG. 6, and the reset voltage application period is set to three times the scanning period τ.
The application state of the scanning voltage to the light modulation elements in each scanning line in this case is as shown in the chart of FIG. According to FIG. 7, as in the case of the first embodiment, the selection voltage is applied immediately after the selection voltage application period in the i-th scanning line ends in the i + 1-th scanning line. In this case, the reset voltage application period of the (i + 1) th row overlaps with the selection voltage application period of the i-th row and a period before that (a part of the reset voltage application period in the figure). But they are overlapped as well.
[0051]
As described above, by extending the reset voltage application period, it is possible to obtain accurate responsiveness without increasing the scanning period even for a light modulation element having a long recovery time.
[0052]
Here, FIG. 8 shows a chart of the response of the applied voltage Vgs and the transmitted light to the pixel Tr (1,1) and the pixel Tr (1,2) of the present embodiment. As shown in FIG. 8 (a), the pixel Tr (1,1) ends the fall time τf within the reset period of the pixel, and a signal for turning on the pixel is applied after the pixel is reset in advance. ing. For this reason, the pixel can be turned on only by the rise time τr.
Further, as shown in FIG. 8B, the pixel Tr (1, 2) ends the falling time τf within the reset period of the pixel and maintains the state thereafter, thereby turning the pixel off.
[0053]
As shown in the above embodiments, the light modulation element preferably has a configuration in which the light modulation element is in an equilibrium state (returned state) or a reset state is light blocking. If the reset state is the ON (light transmission) state of the element, when “black” is output as a pixel, light transmission occurs due to the reset operation, and the contrast is remarkably deteriorated.
On the other hand, if the reset state is OFF (light blocking), there is no light transmission at the time of “black” output, and the contrast hardly changes. In the case of “white” output, the output decreases only during the reset period. In this case, there is almost no visual problem. This is because, for example, in the case of a panel having 500 to 1000 rows, even when the reset period is for several rows, the light amount decrease due to this is as small as about 1%. Also, since the response of the device itself is slow, the output does not immediately turn from ON to OFF, but gradually diminishes, and human visual characteristics are insensitive to luminance changes when the background luminance is high. But there is.
[0054]
As described above, in each of the above embodiments, the light modulation element using the light guide diffusion action shown in FIG. 1 is used. However, the drive system according to the present invention is not limited to this, and light modulation by light guide reflection is used. It can also be applied to elements. This is a configuration in which a reflective film made of aluminum or the like that is moderately inclined is provided on the diaphragm to make it a flexible thin film, and the light guided to the flexible thin film when the voltage is on is reflected to the light guide plate side by the reflective film. It is a light modulation element that reflects and emits light. In addition, the present invention can also be applied favorably to the following light modulation elements.
Hereinafter, other respective configuration examples of the light modulation element in the flat display device in each of the above-described embodiments will be sequentially described with reference to FIGS.
[0055]
First, an example using Fabry-Perot interference will be described as an operation principle for optical modulation of a flexible thin film by electromechanical operation. In Fabry-Perot interference, in a state where two planes are arranged in parallel to each other, incident light is repeatedly reflected and transmitted and divided into a number of light beams, which are parallel to each other. The transmitted light overlaps and interferes at infinity. If the angle between the surface and the perpendicular incident ray is i, the optical path difference between adjacent rays is given by x = nt · cosi. However, n is a refractive index between two surfaces, and t is an interval. If the optical path difference x is an integral multiple of the wavelength λ, the transmission lines reinforce each other, and if the optical path difference x is an odd multiple of the half wavelength, they cancel each other. That is, if there is no phase change during reflection,
2nt · cosi = mλ is the maximum transmitted light,
2nt · cosi = (2m + 1) λ / 2 and the transmitted light is minimized.
However, m is a positive integer.
[0056]
That is, by moving the flexible thin film so that the optical path difference x becomes a predetermined value, the light emitted from the transparent substrate can be modulated and emitted from the flexible thin film.
[0057]
A specific configuration in which a light modulation element using such Fabry-Perot interference is combined with a flat light source to form a flat display will be described below.
FIG. 9 is a schematic cross-sectional view of the light modulation element and the planar light source. The light modulation element 20 displaces the diaphragm 22 by applying a voltage to a substrate upper electrode (not shown) provided on a substrate 21 transparent to ultraviolet rays and a diaphragm upper electrode (not shown) provided on the diaphragm 22, By causing the interference effect, the ultraviolet light from the planar light source 23 is modulated.
[0058]
The flat light source 23 includes a flat flat light source unit 23a and a black light ultraviolet lamp (low pressure mercury lamp) 23b provided on the side of the flat light source unit 23a. The flat light source 23 causes the ultraviolet light from the low pressure mercury lamp 23b for black light to enter from the side surface of the flat light source unit 23a and to exit from the upper surface.
A fluorescent material for black light (for example, BaSi) is formed on the inner wall of the low-pressure mercury lamp 23b. ₂ O _Five : Pb ²⁺ ) Is applied, the spectral characteristics of the emitted ultraviolet rays are such that the center wavelength λ is around 360 nm as shown in FIG. ₀ Have This ultraviolet light is used as backlight light.
[0059]
A pair of substrate electrodes (not shown) is provided on the substrate 21 at a predetermined interval in the direction perpendicular to the plane of FIG. Dielectric multilayer mirrors 25 and 26 are provided between the electrodes on the substrate 21.
[0060]
The diaphragm 22 is suspended at both ends by a support portion 24 formed on the substrate 21 and is provided at a predetermined interval from the substrate 21. A dielectric multilayer mirror 25 is provided on the lower surface of the diaphragm 22 so as to face the dielectric multilayer mirror 26 on the substrate 21 with a predetermined gap t.
[0061]
In the light modulation element 20 configured as described above, the interval between the gaps 27 when the applied voltage to each electrode is turned off is toff (the state on the left side in FIG. 9). In addition, when the voltage is applied, the interval between the gaps 27 is shortened by the electrostatic force, which is set to ton (state shown on the right side of FIG. 9). Ton is appropriately set by balancing the electrostatic force acting on the diaphragm 22 with the application of voltage to each electrode and the restoring force generated with the deformation of the diaphragm 22.
[0062]
In order to perform more stable control, a spacer (not shown) is provided on the electrode, and the displacement of the diaphragm 22 is physically restricted by the spacer, so that the displacement amount of the diaphragm 22 is constant. When the spacer is an insulator, an effect of reducing the voltage applied to each electrode is produced by its relative dielectric constant (1 or more). In addition, this effect is further increased when the spacer is conductive. The spacer may be formed of the same material as each electrode.
[0063]
Here, ton and toff are set as follows. (M = 1)
ton = 1/2 × λ ₀ = 180nm (λ ₀ : Center wavelength of ultraviolet rays)
toff = 3/4 × λ ₀ = 270nm
[0064]
The dielectric multilayer mirrors 25 and 26 each have a light intensity reflectance of R = 0.85. The air gap 27 is made of air or a rare gas, and its refractive index is n = 1. Since the ultraviolet rays are collimated, the incident angle i (the angle formed between the perpendicular of the dielectric multilayer mirror surface and the incident light beam) incident on the light modulation element 20 is substantially zero. The light intensity transmittance of the light modulation element 20 at this time is as shown in FIG.
[0065]
Therefore, toff = 270 nm when no voltage is applied to each electrode, and the light modulation element 20 hardly transmits ultraviolet rays.
On the other hand, when a voltage is applied to each electrode to set ton = 180 nm, the light modulation element 20 transmits ultraviolet rays.
[0066]
If the interference condition is satisfied, the gap t of the air gap 27, the refractive index n, the light intensity reflectivity R of each dielectric multilayer mirror 25, 26, etc. may be any combination.
If the gap t is continuously changed according to the voltage value, the center wavelength of the transmission spectrum can be arbitrarily changed. Thereby, it is also possible to control the amount of transmitted light continuously. That is, gradation control by changing the applied voltage between the electrodes is possible.
[0067]
As a modification of the light modulation element 20, a backlight using a low-pressure mercury lamp may be used instead of the black light mercury lamp 23b.
That is, a backlight unit is configured by combining a low-pressure mercury lamp whose main component is a line spectrum of 254 nm with a transparent substrate made of quartz glass or the like. Other wavelengths are cut by a filter or the like. The spectral characteristics of the ultraviolet backlight at this time are as shown in FIG.
In this light modulation element, the constituent material (diaphragm, dielectric multilayer mirror, substrate, etc.) of the effective pixel area is a material that transmits ultraviolet light of 254 nm.
[0068]
Here, ton and toff are set as follows. (M = 1).
ton = 1/2 × λ ₀ = 127 nm (λ ₀ : Center wavelength of ultraviolet rays)
toff = 3/4 × λ ₀ = 191 nm
[0069]
Other conditions are R = 0.85, n = 1, and i = 0 as in the above example. The light intensity transmittance of the light modulation element at this time is as shown in FIG.
Therefore, toff = 191 nm when no voltage is applied to each electrode, and the light modulation element transmits almost no ultraviolet light, and when a voltage is applied, ton = 127 nm, and the light modulation element transmits ultraviolet light.
[0070]
In particular, in the case of this modified example, since ultraviolet rays are a line spectrum, it exhibits a very high energy transmittance, and modulation with high efficiency and high contrast is possible.
Also in this modification, any combination of the spacing t of the air gap 27, the refractive index n, the light intensity reflectance R of each dielectric multilayer mirror 25, 26, etc. may be used as long as the interference condition is satisfied.
[0071]
Furthermore, if the gap t is continuously changed by changing the voltage value applied to each electrode, the center wavelength of the transmission spectrum can be arbitrarily changed. As a result, the amount of transmitted light can be continuously controlled. That is, gradation control can be performed by changing the voltage applied to each electrode.
[0072]
Next, another modification of the light modulation element will be described with reference to FIG.
FIG. 14 is a schematic cross-sectional view of the light modulation element and the planar light source. The light modulation element 30 performs light modulation by displacing the light shielding plate 31 by electrostatic stress accompanying voltage application to the light shielding plate 31 and the transparent electrode 32 and changing the path of ultraviolet rays from the flat light source 33. The configuration of the planar light source 33 is the same as that of the planar light source 23 shown in FIG.
[0073]
The transparent electrode 32 is provided on a substrate 34 that transmits ultraviolet rays and transmits ultraviolet rays. An insulating light shielding film 35 is provided on the substrate 34 other than the transparent electrode 32. An insulating film 36 is laminated on the top surfaces of the transparent electrode 32 and the light shielding film 35.
[0074]
The light shielding plate 31 is provided as a cantilever structure with a predetermined distance from the substrate 34 above the substrate 34 via a support column 37 erected on the substrate 34. The shape of the light shielding plate 31 corresponds to the shape of the transparent electrode 32 on the opposing substrate 34 and is slightly larger than the transparent electrode 32.
[0075]
The light shielding plate 31 is made of a flexible thin film having conductivity, and is made of, for example, a single conductive thin film made of a material that absorbs or reflects ultraviolet rays, or a plurality of conductive thin films.
Specific examples include a single-layer structure made of a semiconductor such as a metal thin film such as aluminum or chromium that reflects ultraviolet rays, or polysilicon that absorbs ultraviolet rays. Further, a configuration in which a metal is deposited on an insulating film such as silicon oxide or silicon nitride, a semiconductor thin film such as polysilicon, or a composite configuration in which a filter such as a dielectric multilayer film is deposited may be employed.
[0076]
The light modulation element 30 configured as described above operates as follows. In the light modulation element 30, when no voltage is applied between the light shielding plate 31 and the transparent electrode 32, the light shielding plate 31 faces the transparent electrode 32, and the ultraviolet light transmitted through the transparent electrode 32 is absorbed or reflected by the light shielding plate 31. (The state on the left side of FIG. 14).
[0077]
On the other hand, when a voltage is applied between the light shielding plate 31 and the transparent electrode 32, the light shielding plate 31 is displaced to the transparent electrode 32 side while being twisted by the electrostatic force acting between them (state on the right side in FIG. 14). As a result, the ultraviolet light transmitted through the transparent electrode 32 from the planar light source 33 is emitted upward without being shielded by the light shielding plate 31.
When the voltage applied between the light shielding plate 31 and the transparent electrode 32 is set to zero again, the light shielding plate 31 returns to the initial position due to the elasticity of the light shielding plate 31 itself and the column 37.
[0078]
Next, another modification of the light modulation element will be described with reference to FIGS.
15 is a schematic configuration diagram of the light modulation element 40, FIG. 15 (a) is a plan view, and FIG. 15 (b) is a cross-sectional view taken along line BB of FIG. 15 (a).
[0079]
The light modulation element 40 displaces the electrode light-shielding plate 43 in the left-right direction in FIG. Light is blocked or transmitted.
[0080]
The counter electrodes 41 and 42 are opposed to each other at a predetermined interval on a substrate 44 that transmits ultraviolet rays, and two pairs are provided in parallel in FIG. Further, a light shielding film 45 is provided between the counter electrodes 42 on the right side of FIG.
[0081]
The electrode light shielding plate 43 is provided so as to be displaceable in the left-right direction at a position spaced apart from the substrate 44 above the substrate 44 in FIG. That is, the left and right sides of the electrode light shielding plate 43 are supported by the support portion 47 via flexible members such as a polygonal line spring 46. The electrode light-shielding plate 43 is displaced in the left-right direction in FIG. 15 while the polygonal line spring 46 is elastically deformed by electrostatic force accompanying voltage application to the counter electrodes 41 and 42. The dimension of the electrode light-shielding plate 43 in the left-right direction is approximately half of the distance along the left-right direction between the support portions 47.
[0082]
The light modulation element 40 configured as described above operates as follows. That is, in the light modulation element 40, when a voltage is applied only to the counter electrode 41 on the left side of FIG. 15 with the voltage zero applied to the electrode light shielding plate 43, the electrode light shielding plate 43 is moved to the left side of FIG. It moves between the counter electrodes 41 (state shown in FIG. 15). Thereby, the light emitted from the planar light source and transmitted through the substrate 44 without being shielded by the light shielding film 45 is shielded by the electrode light shielding plate 43.
[0083]
On the other hand, when a voltage of + V is applied to the electrode light-shielding plate 43 and a voltage is applied only to the counter electrode 41 on the left side of FIG. 16, the electrode light-shielding plate 43 is placed between the counter electrode 42 on the right side of FIG. Move (state shown in FIG. 16). Thus, the light emitted from the planar light source and transmitted through the substrate 44 without being shielded by the light shielding film 45 is emitted upward in FIG. 16B without being shielded by the electrode light shielding plate 43.
When the applied voltage is set to zero again, the electrode light shielding plate 43 returns to the initial position by the elastic force and electrostatic force of the polygonal line spring 46.
As described above, configurations of various light modulation elements are conceivable. However, the present invention is not limited to the above-described configurations, and may have any other configuration as long as it has an equivalent function. .
[0084]
【The invention's effect】
As described above, according to the present invention, the electromechanical light modulation elements that perform light modulation by the displacement operation of the flexible portion by electrostatic force and the elastic return operation of the flexible portion are arranged in a two-dimensional matrix. The array-type light modulation element driving method according to the first aspect of the present invention is directed to a reset scan that performs a return operation of the light modulation element, and a write operation that selects an element displacement operation or a state maintenance for a scan line other than the reset scan line. The scanning is performed simultaneously with scanning, and writing scanning for each scanning line is performed without interruption. As a result, even a light modulation element having a long elastic recovery time can display an image at a higher speed without losing time, and the response time can be dramatically improved.
[0085]
In addition, by setting the drive time for reset scanning of the light modulation element to be equal to or longer than the elastic recovery time such as an integral multiple of the write scanning time, even a light modulation element that requires a long time for elastic recovery operation loses time. High-speed response can be obtained with appropriate scanning.
[0086]
In addition, a planar light source that emits ultraviolet light is provided opposite to the array type light modulation element in which electromechanical light modulation elements are arranged in a matrix, and a phosphor is placed on the opposite side of the plane light source across the array type light modulation element. By providing and driving the flat display by causing the phosphor to emit light by the light emitted from the light modulation element, a flat display having high-speed response without reducing the contrast can be obtained.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a light modulation operation of a light modulation element according to a first embodiment of the present invention.
FIG. 2 is a plan view of an array type light modulation element in which the light modulation elements shown in FIG. 1 are two-dimensionally arranged.
FIG. 3 is an explanatory diagram showing a relationship between a combination of a scan electrode voltage and a signal electrode voltage and an interelectrode voltage of a light modulation element.
FIG. 4 is an explanatory diagram of a method for writing data by applying a voltage having a different waveform to each light modulation element in the first embodiment.
FIG. 5 is a chart for explaining that the drive period of the reset operation in the first embodiment is performed simultaneously with the write operation of the row before scanning.
FIG. 6 is an explanatory diagram of a method for writing data by applying a voltage having a different waveform to each light modulation element in the second embodiment.
FIG. 7 is a chart for explaining that the drive period of the reset operation in the second embodiment is performed simultaneously with the write operation of the row before scanning.
FIG. 8 is an explanatory diagram showing response characteristics of transmitted light from a light modulation element.
FIG. 9 is an operation explanatory diagram of a light modulation element using a multilayer interference effect.
FIG. 10 is a graph showing spectral characteristics of a backlight using a low-pressure mercury lamp.
11 is a graph showing the light intensity transmittance of the light modulation element when the backlight having the characteristics shown in FIG. 10 is used.
FIG. 12 is a graph showing spectral characteristics of an ultraviolet backlight.
FIG. 13 is a graph showing the light intensity transmittance of the light modulation element.
FIG. 14 is a schematic cross-sectional view of another modification of the light modulation element and the planar light source.
FIG. 15 is a diagram illustrating a configuration and a light shielding operation in another modification of the light modulation element.
16 is a diagram for explaining a light guide state of the light modulation element shown in FIG. 15;
FIG. 17 is a diagram illustrating a hysteresis characteristic of light transmittance with respect to an applied voltage of an electromechanical light modulation element.
FIG. 18 is a diagram illustrating response characteristics of transmitted light with respect to an applied voltage of a light modulation element.
[Explanation of symbols]
1 Light guide plate
2 signal electrodes
4 Diaphragm
7 Signal electrode
8 Flexible thin film
10, 20, 30 Light modulation element
50 Array type light modulator
τ Scanning time for one line
τr rise time
τf Fall time

Claims (6)

In an array type light modulation element in which electromechanical light modulation elements that perform light modulation by an elastic force displacement operation by an electrostatic force and an elastic return operation of the flexible part are arranged in a two-dimensional matrix,
The reset scan for performing the return operation of the light modulation element is performed simultaneously with the write scan for selecting the displacement operation or the state maintenance for the scan lines other than the reset scan line, and the write scan for each scan line. A method for driving an array type light modulation element, wherein the driving is performed without interruption. 2. The method of driving an array type light modulation element according to claim 1, wherein the reset scanning time is set to an integral multiple of the writing scanning time. 3. The array type light modulation device driving method according to claim 1, wherein a driving time of the reset scanning is set to be equal to or longer than an elastic return time of the flexible portion. 4. The array type light modulation element driving method according to claim 1, wherein the elastic return operation of the light modulation element is an operation in which a light shielding state is achieved after the return. The array-type light modulation element, a planar light source disposed opposite to the array-type light modulation element, and a phosphor disposed on the opposite side of the planar light source across the array-type light modulation element,
The array type light modulation element is driven by the driving method according to any one of claims 1 to 4, and the phosphor is lit and displayed by the light emitted from the array type light modulation element. To drive a flat display. 6. The method of driving a flat display according to claim 5, wherein the flat light source is an ultraviolet light emission light source that excites the phosphor.

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